Multi-acid polymers and methods of making the same

ABSTRACT

A multi-acid monomer disclosed herein has the formula 
                         
wherein R is one or more units of a non-SO 2 F or non-SO 2 Cl portion of a polymer precursor in sulfonyl fluoride or sulfonyl chloride form, X is a non-sulfonyl halide group of a multi-sulfonyl halide compound having a minimum of two acid giving groups, and Y is remaining sulfonyl halide groups of the multi-sulfonyl halide compound.

TECHNICAL FIELD

This disclosure relates to multi-acid monomers from multifunctionalamino acids and sulfonyl halide precursors and methods of making themulti-acid monomers and polymers.

BACKGROUND

Proton exchange membrane fuel cells (PEMFCs) generate power fromelectrochemical conversion of fuels, such as hydrogen and hydrocarbons,at their anodes and oxidants, such as oxygen and air, at their cathodesusing the polymer membrane as electrolyte. The membrane acts both as aproton conductor from anode to cathode and a barrier between fuels andoxidants. Current state-of-art membranes such as Nafion™ membranes,Aquivion™ membranes, and low equivalent weight (EW) perfluorosulfonicacid (PFSA) membranes have only one sulfonic acid group in the sidechain. As a result, these membranes hold little water at any givenrelative humidity (RH %) and have very low ionic conductivity,especially at low RH % and at temperatures below 100° C.

SUMMARY

Disclosed herein are multi-acid monomers and multi-acid membranes, andmethods of making the multi-acid monomers and multi-acid membranes.

A multi-acid monomer disclosed herein has the formula

wherein R is one or more units of a non-SO₂F or non-SO₂Cl portion of apolymer precursor in sulfonyl fluoride or sulfonyl chloride form, X is anon-sulfonyl halide group of a multi-sulfonyl halide compound having aminimum of two acid giving groups, and Y is remaining sulfonyl halidegroups of the multi-sulfonyl halide compound.

Also disclosed are methods of making the multi-acid monomers. A methodcomprises reacting a polymer precursor in sulfonyl fluoride or sulfonylchloride form with anhydrous ammonia to obtain a sulfonamide, whereinthe polymer precursor in sulfonyl fluoride or sulfonyl chloride form hasa formula R—SO₂F or R_(f)—SO₂Cl, respectively, with R being one of moreunits of the polymer precursor without sulfonyl fluoride or sulfonylchloride, and wherein the sulfonamide has a formula R_(f)—SO₂—NH₂; andreacting the sulfonamide with a multi-sulfonyl halide compound having aminimum of two acid giving groups under a mild base condition to form anintermediate polymer in sulfonyl halide form. The intermediate polymeris hydrolyzed with a base and an alcohol and ion exchanged with an acidto produce the multi-acid monomer with a following formula:

wherein R is the one of more units of the polymer precursor withoutsulfonyl fluoride or sulfonyl chloride, X is the non-sulfonyl halidegroup of the multi-sulfonyl halide compound, and Y is the remainingsulfonyl halide groups of the multi-sulfonyl halide compound.

These and other aspects of the present disclosure are disclosed in thefollowing detailed description of the embodiments, the appended claimsand the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying drawings. It isemphasized that, according to common practice, the various features ofthe drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.

FIG. 1 is a flow diagram of a method of making a multi-acid monomer asdisclosed herein.

FIG. 2 is a flow diagram of the method of making the multi-acid polymerand a multi-acid membrane as disclosed herein.

FIG. 3 is a flow diagram of another method of making a multi-acidmonomer as disclosed herein.

FIG. 4 is a flow diagram of a method of making an imide and sulfonicacid fluorinated monomer as disclosed herein.

FIG. 5 is a flow diagram of a method of making an imide and phosphonicacid fluorinated monomer as disclosed herein.

FIG. 6 is a flow diagram of another method of making a multi-acidmonomer as disclosed herein.

DETAILED DESCRIPTION

Membranes that incorporate more acid groups for high ionic conductivity,especially at low RH % and at typical PEMFCs operating temperature, willenable simplified humidification systems, will improve performance ofthe fuel cell, and will reduce the cost for early commercialization ofPEMFC electric vehicles. The multi-acid monomers disclosed herein,having two or more proton conducting sites, provide such membranes.

Ionic conductivity of membranes at low RH % is improved by increasingthe acid groups in the membrane, such as sulfonic acids (—SO₃H group),imide acids (SO₂—NH—SO₂ group), and phosphonic acids (PO₃H group).Increasing the acid groups reduces the equivalent weight (EW) because EWis inversely proportional to acid quantity in the membrane. However,increasing the acid groups by more than one in the side group in thecurrent state-of-the-art membranes has been extremely difficult andchallenging. The current membranes in the precursor form (SO₂F) haveonly one SO₂F group that is hydrolyzed and ion-exchanged to accomplishonly one SO₃H group per side chain. Since, only one SO₃H acid group perside chain is attained in the current membranes, the water uptake, ionicconductivity, IV performance, and power density are limited in suchmembranes that have applications in hydrogen and hydrocarbon PEMFCs.Additionally, because of limits on reactivity of typical startingmonomers and co-monomers, such as tetrafluoroethylene (CF₂═CF₂) monomerand perfluoro (3-oxapent-4-ene) sulfonyl fluoride and perfluoro(4-methyl-3,6-dioxaoct-7-ene)sulfonyl fluoride, increasing the acidgroup or reducing the EW below certain values, such as EW 1100, EW 870,EW 725, is difficult and expensive. Current state-of-the-art PFSAmembranes that have just one sulfonic acid group are already expensive.Modifying such PFSA membranes to incorporate multi-acid groups currentlyrequires sophisticated equipment and extremely high reaction conditions.

Currently, monomers having multiple acids or capable of holding multipleacids are non-existent for application in PEMFC membranes. In the PEMFCindustry, it has been very challenging to develop membranes havingphosphonic acid. Attempts to develop membranes with phosphonic acids forhigh temperature PEMFCs have been unsuccessful. Doping methods have beenused to add phosphonic acids into the membrane; however, the phosphonicacids can leach from the membranes. The methods disclosed hereinincorporate amino phosphonic acids into a polymer matrix, covalentlyattaching phosphonic acid to the polymer to produce a robust and stablemembrane.

Multi-acids in the side group enable higher water uptake, higher ionicconductivity and higher power density in PEMFCs. The methods disclosedherein produce such multi-acid membranes. Some methods link variousamino acids having multiple sulfonic acids or phosphonic acids withmonomers, copolymers or polymers in sulfonyl fluoride or sulfonylchloride (SO₂F/Cl) form to produce polymer electrolyte membranes ormaterials with high acid content for application in PEMFCs. An aminoacid with more than one acid group is linked with a monomer, copolymeror polymer in SO₂F/Cl form to produce multi-acid membranes. Methodsdisclosed herein use amino acid compounds that have a primary aminegroup (—NH₂) attached to multiple sulfonic acids or phosphonic acids.The methods incorporate varieties of amino sulfonic acids or aminophosphonic acids or amino sulfonyl halides that are highly acidic.

Embodiments of the multi-acid membranes disclosed herein can besynthesized at mild reaction conditions using inexpensive, commerciallyavailable amino sulfonic or amino phosphonic acids. Other embodiments ofthe multi-acid membranes disclosed herein are synthesized usingammonolysis and sulfonyl halide compounds, with the side group in thepolymer chain extended to incorporate many acid groups that will resultin very high acidic polymer electrolyte membranes. These multi-acidmonomers and polymers produce robust, highly acidic, and highlyefficient polymer electrolyte membranes with extremely low EW forapplications, including applications in low RH %.

The methods and materials disclosed herein can be used to producepolymer electrolyte membranes for direct alcohol PEMFCs, directhydrocarbons PEMFCs, other PEMFCs, for various ion-exchange processessuch as Chlor-Alkali processes, water purification, desalinationprocesses, electrolytes for lithium-ion batteries and redox flowbatteries and for acid catalysis in organic synthesis.

The monomers, polymers, or copolymers in SO₂F/Cl form and varioussulfonyl halide compounds discussed herein are converted into new typesof monomers, polymers or copolymers having multiple sulfonyl halidegroups. These new monomers, polymers or copolymers can be copolymerizedwith other compatible monomers, polymers or copolymers to createvarieties of new families of copolymers.

There are a variety of monomers, polymers or copolymers in SO₂F/Cl formthat can be converted into corresponding monomers, polymers orcopolymers having multiple sulfonic acids, imide acids and/or phosphonicacids. As used herein, “polymer precursors in SO₂F/Cl form” includesmonomers, polymers, copolymers, resins and membranes in SO₂F/Cl formthat can be used as a starting material to produce the multi-acidmonomers, polymers and membranes disclosed herein. Any fluorinated,partially fluorinated, chlorinated, partially chlorinated or hydrocarbonpolymer, copolymer or monomer can be used. Non-limiting examplesinclude: Nafion™ polymer or resins in SO₂F form; Aquivion™ polymer orresins in SO₂F form; polymer, copolymer or monomer of2-Allyloxy-1,1,2,2-tetrafluoro ethane sulfonyl fluoride; polymer,copolymer or monomer of 4-(trifluorovinyl) benzene sulfonyl fluoride;polymer, copolymer or monomer of p-styrene sulfonyl fluoride/chloride;polymer, copolymer or monomer of perfluoro (3-oxapent-4-ene) sulfonylfluoride; polymer, copolymer or monomer of ethene sulfonyl fluoride;polymer, copolymer or monomer of 2-propene-1-sulfonyl chloride; andpolymer, copolymer or monomer of perfluoro (4-methyl-3,6-dioxaoct-7-ene)sulfonyl fluoride.

One embodiment of a multi-acid monomer disclosed herein has thefollowing formula (1): R—SO₂—NH—(SO₃ ⁻H⁺)_(n), wherein R=one or moreunits of the polymer precursor without sulfonyl fluoride or sulfonylchloride and n=the number of acid sites from the amino acid havingsulfonic acids used to make the multi-acid polymer. The multi-acidmonomers are multi-sulfonic acid fluorinated monomers.

For example, when the amino acid used is 7-aminonaphthalene 1, 3,5-trisulfonic acid, having the following formula:

the multi-acid monomer has n=3, four proton conducting groups, and thefollowing formula (2):

R has, for example, the following formula:

wherein R_(f)=—CF₂—CF(CF₃)—O—(CF₂)₂—, —(CF₂)₄—, or —(CF₂)₂—, n=1 or moreand m=3-13.5. For example, when the polymer precursor is Nafion™, n=1and m=5-13.5. When the polymer precursor is Aquivion™, n=1 and m=3-7.

A method of making the multi-acid monomer in formula (1) is alsodisclosed. The method comprises reacting an amino acid having multiplesulfonic acids with a polymer precursor in SO₂F/Cl form in a mild basecondition. To produce the multi-acid monomer of formula (2), which hasfour proton conducting groups, the amino acid used is 7-aminonaphthalene1, 3, 5-trisulfonic acid, with n=3, the equation shown below.

The formulas of examples of polymer precursors R—SO₂F/Cl that willproduce the multi-acid monomer shown in formula (2) are shown below:

The method of making the multi-acid monomer and polymer can be performedin various orders. For example, the polymer precursor can be a polymeror co-polymer that does not need to be polymerized. The polymerprecursor can be a polymer or co-polymer that requires additionalpolymerization. The polymer precursor can be a monomer that will requirepolymerization, such as when R is one unit. Polymerization can occurprior to producing the multi-acid groups. The polymer precursor can bereacted to form the multi-acid groups and then polymerized. The polymerprecursor can be polymerized or not, and formed into a membrane, withthe membrane reacted to form the multi-acid groups. Any combination ofsteps is contemplated herein.

Using this one step synthesis shown in FIG. 1, the polymer precursorhaving only one SO₂F/Cl group in the side group in step 10 can beconverted into the multi-acid monomer in step 12 shown in formula (1)and membranes having many sulfonic acid groups. In addition to7-aminonaphthalene 1, 3, 5-trisulfonic acid mentioned above, there areother amino acid compounds having multiple sulfonyl acids that can beused to produce the multi-acid monomers. Non-limiting examples include:2-naphthylamine-3,6,8-trisulfonic acid; sulfanilamide;1-naphthylamine-3,6,8,-trisulfonic acid disodium salt hydrate;8-aminonaphthalene-1,3,6-trisulfonic acid disodium salt; 5-aminonaphthalene-1,3,6-trisulfonic acid; 8-aminopyrene-1,3,6-trisulfonic acidtri sodium salt; sodium 2-amino-4-sulfobenzene 1-sulfonate; sodium3-amino-4-sulfobenzene-1-sulfonate; sodium2-amino-5-sulfobenzene-1-sulfonate;4-Amino-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salthydrate; disodium 4-amino-5-sulfonaphthalene-2,7-disulfonate;3-aminonaphthalene-1,5-disulfonic acid;2-amino-4,8-naphthalenedisulfonic acid;4-amino-6-chlorobenzene-1,3-disulfonyl dichloride; 4-(aminosulfonyl)benzene sulfonyl chloride; 6-aminopyridine-3-sulfonic acid;4-aminopyridine-3-sulfonic acid; 2-aminopyridine-5-sulfonic acid;2-aminopyridine-3-sulfonic acid; 7-amino-1,3-naphthalenedisulfonic acidmonopotassium salt monohydrate;1-amino-8-hydroxynaphthalene-3,6-disulfonic acid; and 2,4,6-trischlorosulfonyl aniline.

Another embodiment of a multi-acid monomer disclosed herein has thefollowing formula (3): R—SO₂—NH—(PO₃ ⁻H²⁺)_(n), wherein R=one or moreunits of the polymer precursor without sulfonyl fluoride or sulfonylchloride and n=the number of acid sites from the amino acid havingphosphonic acids used to make the multi-acid polymer. The multi-acidmonomer is a multi-phosphonic acid fluorinated monomer. Multi-phosphonicacid fluorinated polymers are beneficial in making membranes that canoperate at high temperatures because phosphoric acid becomes more protonconductive at high temperatures.

For example, when the amino acid used is1-aminopropane-1,1,3-triphosphonic acid, the multi-acid monomer has n=3,seven proton conducting groups, and the following formula (4):

R has, for example, the following formula:

wherein R_(f)=—CF₂—CF(CF₃)—O—(CF₂)₂—, —(CF₂)₄—, or —(CF₂)₂—, n=1 or moreand m=3-13.5.

A method of making the multi-acid monomer in formula (3) is alsodisclosed. The method comprises reacting an amino acid having multiplephosphonic acids with a polymer precursor in SO₂F/Cl form in a mild basecondition.

To produce the multi-acid monomer of formula (4), which has seven protonconducting groups, the amino acid used is1-aminopropane-1,1,3-triphosphonic acid, with n=3, with the equationshown below.

Using this one step synthesis shown in FIG. 1, the polymer precursorhaving only one SO₂F/Cl group in the side group in step 10 can beconverted into the multi-acid monomer in step 12 shown in formula (3)and membranes having many phosphonic acid groups. In addition to1-aminopropane-1,1,3-triphosphonic acid mentioned above, there are otheramino acid compounds having multiple sulfonyl acids that can be used toproduce the multi-acid monomers. Non-limiting examples include(4-amino-1-hydroxybutane-1,1-diyl) diphosphonic acid,1-amino-2,2,2-trifluoroethyl) phosphonic acid and 1-aminopropane-1,1-diphosphonic acid.

As noted, the method of making the multi-acid monomer and polymer can beperformed in various orders. For example, the polymer precursor can be apolymer or co-polymer that does not need to be polymerized. The polymerprecursor can be a polymer or co-polymer that requires additionalpolymerization. The polymer precursor can be a monomer that will requirepolymerization, such as when R is one unit. Polymerization can occurprior to producing the multi-acid groups. The polymer precursor can bereacted to form the multi-acid groups and then polymerized. The polymerprecursor can be polymerized or not, and formed into a membrane, withthe membrane reacted to form the multi-acid groups. Any combination ofsteps is contemplated herein.

The reaction between sulfonyl halides and secondary amine groups isfacile under mild basic conditions. As shown in FIG. 2, the polymerprecursor in SO₂F/Cl form can be soaked in a solvent such asacetonitrile, water or any other organic solvent in step 20. A mild basecondition is formed by adding a base in step 22 such as pyridine, K₂CO₃,KOH or NaOH. The amino acid is added to the mixture in step 24. In step26, the reaction is performed below 100° C. for at least twelve hours toachieve satisfactory conversion to the multi-acid monomer. Inparticular, the reaction is performed at a temperature between about 90°C. and 100° C. The multi-acid monomer can be retrieved from the reactionvessel and rinsed with deionized water several times in step 28 and thenboiled in deionized water to remove any trace of residuals from thereaction in step 30.

A membrane for a PEMFC can be made from the multi-acid polymer. Themulti-acid polymer is shaped into membrane form. To fully convert themulti-acid polymer to a membrane in acid form, the multi-acid polymer ision-exchanged in step 32. For example, the multi-acid polymer can beion-exchanged twice with 1-2 M aqueous sulfuric acid solution for aminimum of two hours at 80-100° C. and then rinsed with deionized waterseveral times and boiled in deionized water to obtain the membrane incomplete multi-acid form.

Another multi-acid monomer as disclosed herein is produced from the samepolymer precursors discussed above. The multi-acid monomer has thefollowing formula (5):

wherein R is one or more units of a non-SO₂F or non-SO₂Cl portion of thepolymer precursor in sulfonyl fluoride or sulfonyl chloride form. Themulti-acid monomer is an imide and sulfonic acid fluorinated monomer.

Another multi-acid monomer as disclosed herein has the following formula(6):

wherein R is one or more units of a non-SO₂F or non-SO₂Cl portion of thepolymer precursor in sulfonyl fluoride or sulfonyl chloride form. Themulti-acid monomer is an imide and phosphonic acid fluorinated polymer.

A method of making the multi-acid monomers shown in formulas (5) and (6)is illustrated in FIG. 3. The method comprises reacting a polymerprecursor in sulfonyl fluoride or sulfonyl chloride form with anhydrousammonia to obtain a sulfonamide in step 100. The polymer precursor insulfonyl fluoride or sulfonyl chloride form has a formula R—SO₂F orR—SO₂Cl, respectively, with R being one of more units of the polymerprecursor without sulfonyl fluoride or sulfonyl chloride, as discussedherein with reference to the multi-sulfonic acid fluorinated monomer andthe multi-phosphonic acid fluorinated monomer. The sulfonamide has aformula R—SO₂—NH₂. The sulfonamide is reacted with a compound of aformula COOH—X-AGG under a mild base condition in step 102, wherein X isone of C₆H₃ or N(CH₂)₃ and AGG is an acid giving group. This reactionforms the multi-acid monomer having an imide base and more than twoproton conducting groups.

To react the sulfonamide with the compound in step 102, the sulfonamideis soaked in a solvent such as acetonitrile, water or any other organicsolvent. A mild base condition is formed by adding a base such aspyridine, K₂CO₃, KOH or NaOH. The compound is added to the mixture andreacted below 100° C. for at least twelve hours to achieve satisfactoryconversion to the multi-acid monomer. In particular, the reaction isperformed at a temperature between about 90° C. and 100° C. Themulti-imide and sulfonic acid fluorinated monomer can be retrieved fromthe reaction vessel, rinsed with deionized water several times and thenboiled in deionized water to remove any trace of residuals from thereaction.

As noted, the method of making the multi-acid monomer can be performedin various orders. For example, the polymer precursor can be a polymeror co-polymer that does not need to be polymerized. The polymerprecursor can be a polymer or co-polymer that requires additionalpolymerization. The polymer precursor can be a monomer that will requirepolymerization, such as when R is one unit. Polymerization can occurprior to producing the multi-acid groups. The polymer precursor can bereacted to form the multi-acid groups and then polymerized. The polymerprecursor can be polymerized or not, and formed into a membrane, withthe membrane reacted to form the multi-acid groups. Any combination ofsteps is contemplated herein.

One example of the method disclosed above produces an imide and sulfonicacid fluorinated polymer using the compound 3,5-Bis(fluorosulfonyl)benzoic acid having a formula of HOOC—C₆H₃—(SO₂F)₂, where X=C₆H₃ andAGG=(SO₂F)₂. This is illustrated in FIG. 4. In step 110, a polymerprecursor in sulfonyl fluoride form is reacted with ammonia to produce asulfonamide. Reacting the sulfonamide in step 112 with3,5-Bis(fluorosulfonyl) benzoic acid produces an intermediate product:

The intermediate product is hydrolyzed with a base and an alcohol instep 114 and then ion exchanged with an acid in step 116 to form themulti-acid monomer with three proton conducting groups and having thefollowing formula, with R being the one of more units of the polymerprecursor without sulfonyl fluoride or sulfonyl chloride:

A membrane for a fuel cell can be formed from the multi-acid polymer byconverting any remaining sites of the multi-acid polymer to acid form byion-exchanging the multi-acid polymer with sulfuric acid solution toform the multi-acid membrane.

Other compounds of the formula COOH—X-AGG that can be used in the methodof FIG. 4 include, but are not limited to, tris(phosphonomethyl) cyclen;8-acetoxy-pyrene-1, 3, 6-trisulfonyl chloride; 3, 6, 8-trischlorosulfonyl pyrene-1-yl-acetate;7-ethoxycarbonyloxy-naphthaline-1,3,6-trisulfonyl chloride;3,5-bis(chlorosulfonyl) benzoic acid;3,5-bis(chlorosulfonyl)-2-hydroxybenzoic acid; and3,5-bis(chlorosulfonyl)-,methyl ester benzoic acid.

One example of the method disclosed above to produce an imide andphosphonic acid fluorinated polymer is shown in FIG. 5. The polymerprecursor in sulfonyl halide form is reacted with ammonia in step 120 toproduce sulfonamide. The method uses the compound N,N-bis (phosphonomethyl) glycine having a following formula, wherein X=N(CH₂)₂ andAGG=(PO₂H₂ ⁺)₂:

Reacting the sulfonamide with the N,N-bis (phosphono methyl) glycine instep 122 produces the multi-acid monomer having five proton conductinggroups and having the following formula, with R being one of more unitsof the polymer precursor without sulfonyl fluoride or sulfonyl chloride:

A membrane for a fuel cell can be formed from the multi-acid polymer byconverting any remaining sites of the multi-acid polymer to acid form byion-exchanging the multi-acid polymer with sulfuric acid solution toform the multi-acid membrane.

Other compounds of the formula COOH—X-AGG that can be used in the methodof FIG. 5 include, but are not limited to,4-hydroxy-4,4-diphosphonobutanoic acid;1-amino-1,1-diphosphono-2-carboxy ethane; 2,3-diphosphono-propionsaeure;acetic acid, diphosphono-,1-ethyl ester;2-hydroxy-2,3,4-triphosphonobutanoic acid;2-hydroxy-2,3,4-triphosphonobutanoic acid;4-hydroxy-4,4-diphosphonobutanoic acid;2-hydroxy-2,3-diphosphonopropanoic acid;3-(1,1-diphosphonoethylamino)-2-hydroxypropanoic acid;3-amino-2-methyl-3,3-diphosphonopropanoic acid;2-hydroxy-2,3-diphosphonopropanoic acid; 4,4-diphosphonobutanoic acid;4-hydroxy-4,4-diphosphonobutanoic acid; Propanoic acid,3,3-diphosphono-, 1-ethyl ester; 1-amino-1,1-diphosphono-2-carboxyethane.

Another multi-acid monomer disclosed herein has the following formula(7):

R is one or more units of a non-SO₂F or non-SO₂Cl portion of the polymerprecursor in sulfonyl fluoride or sulfonyl chloride form, X is anon-sulfonyl halide group of a multi-sulfonyl halide compound having aminimum of two acid giving groups, and Y is remaining sulfonyl halidegroups of the multi-sulfonyl halide compound. The multi-acid monomer isa multi-imide and sulfonic acid fluorinated polymer.

A method of making the multi-acid monomer in formula (7) is shown inFIG. 6 and comprises reacting the polymer precursor in sulfonyl fluorideor sulfonyl chloride form with anhydrous ammonia to obtain a sulfonamidein step 200, wherein the polymer precursor in sulfonyl fluoride orsulfonyl chloride form has a formula R—SO₂F or R—SO₂Cl, respectively,with R being one of more units of the polymer precursor without sulfonylfluoride or sulfonyl chloride, and wherein the sulfonamide has a formulaR—SO₂—NH₂. In step 202, the sulfonamide is reacted with a multi-sulfonylhalide compound having a minimum of two acid giving groups under a mildbase condition to form an intermediate polymer in sulfonyl halide form.The intermediate polymer is hydrolyzed with a base and alcohol in step204 and is ion exchanged with an acid in step 206 to produce themulti-acid monomer of formula (7), wherein R is the one of more units ofthe polymer precursor without sulfonyl fluoride or sulfonyl chloride, Xis the non-sulfonyl halide group of the multi-sulfonyl halide compound,and Y is the remaining sulfonyl halide groups of the multi-sulfonylhalide compound.

To react the sulfonamide with the multi-sulfonyl halide compound in step202, the sulfonamide is soaked in a solvent such as acetonitrile, wateror any other organic solvent. A mild base condition is formed by addinga base such as pyridine, K₂CO₃, KOH or NaOH. The multi-sulfonyl halidecompound is added to the mixture and reacted below 100° C. for at leasttwelve hours to achieve satisfactory conversion to the multi-acidmonomer. In particular, the reaction is performed at a temperaturebetween about 90° C. and 100° C. The multi-imide and sulfonic acidfluorinated polymer can be retrieved from the reaction vessel, rinsedwith deionized water several times and then boiled in deionized water toremove any trace of residuals from the reaction.

As noted, the method of making the multi-acid monomer can be performedin various orders. For example, the polymer precursor can be a polymeror co-polymer that does not need to be polymerized. The polymerprecursor can be a polymer or co-polymer that requires additionalpolymerization. The polymer precursor can be a monomer that will requirepolymerization, such as when R is one unit. Polymerization can occurprior to producing the multi-acid groups. The polymer precursor can bereacted to form the multi-acid groups and then polymerized. The polymerprecursor can be polymerized or not, and formed into a membrane, withthe membrane reacted to form the multi-acid groups. Any combination ofsteps is contemplated herein.

A membrane for a fuel cell can be formed from the multi-acid polymer byconverting any remaining sites of the multi-acid polymer to acid form byion-exchanging the multi-acid polymer with sulfuric acid solution toform the multi-acid membrane.

Examples of the multi-sulfonyl halide compound include, but are notlimited to, 1,3,5-benzene trisulfonyl chloride, benzene-1,3-disulfonylchloride, benzene-1,2-disulfonyl chloride,perfluorobutane-1,4-bis-sulfonyl chloride,perfluorobutane-1,4-bis-sulfonyl fluoride,1,4-bis(fluorosulfonyloxy)-octafluorobutane, andbis[2-(fluorosulfonyl)tetrafluoroethyl] ether.

When the multi-sulfonyl halide compound is 1,3,5-benzene trisulfonylchloride or 1,3,5-tris[(fluorosulfonyl)] benzene, the multi-acid monomerhas the following formula:

When the multi-sulfonyl halide compound is benzene-1,3-disulfonylchloride or benzene-1,2-disulfonyl chloride, the multi-acid monomer hasthe following formula:

When the multi-sulfonyl halide compound isperfluorobutane-1,4-bis-sulfonyl chloride orperfluorobutane-1,4-bis-sulfonyl fluoride, the multi-acid monomer hasthe following formula:

When the multi-sulfonyl halide compound is1,4-bis(fluorosulfonyloxy)-octafluorobutane, the multi-acid monomer hasthe following formula:

When the multi-sulfonyl halide compound isbis[2-(fluorosulfonyl)tetrafluoroethyl]ether, the multi-acid monomer hasthe following formula:

When the multi-sulfonyl halide compound is1,1,2,2,3,3-hexafluoro-propane-1,3-disulfonyl difluoride, the multi-acidmonomer has the following formula:

When the multi-sulfonyl halide compound is1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane-1,6-disulfonyl fluoride, themulti-acid monomer has the following formula:

When the multi-sulfonyl halide compound is naphthalene-1,2,6-trisulfonylchloride, the multi-acid monomer has the following formula:

While the invention has been described in connection with certainembodiments, it is to be understood that the invention is not to belimited to the disclosed embodiments but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the scope of the appended claims, which scope is to be accordedthe broadest interpretation so as to encompass all such modificationsand equivalent structures as is permitted under the law.

The invention claimed is:
 1. A method of making a multi-acid monomercomprising: reacting a polymer precursor in sulfonyl fluoride orsulfonyl chloride form with anhydrous ammonia to obtain a sulfonamide,wherein the polymer precursor in sulfonyl fluoride or sulfonyl chlorideform has a formula R—SO₂F or R—SO₂Cl, respectively, with R being one ofmore units of the polymer precursor without sulfonyl fluoride orsulfonyl chloride, and wherein the sulfonamide has a formula R—SO₂—NH₂;and reacting the sulfonamide with a multi-sulfonyl halide compoundhaving a minimum of two acid giving groups under a mild base conditionto form an intermediate polymer in sulfonyl halide form; hydrolyzing theintermediate polymer with a base and an alcohol; and ion exchanging theintermediate polymer with an acid to produce the multi-acid monomer witha following formula:

wherein R is the one of more units of the polymer precursor withoutsulfonyl fluoride or sulfonyl chloride, X is the non-sulfonyl halidegroup of the multi-sulfonyl halide compound, and Y is the remainingsulfonyl halide groups of the multi-sulfonyl halide compound.
 2. Themethod of claim 1, wherein reacting the sulfonamide with themulti-sulfonyl halide compound comprises: soaking the sulfonamide in asolvent; adding a base to form the mild base condition; adding themulti-sulfonyl halide compound; and reacting at a temperature of 100° C.or less for a period of time.
 3. The method of claim 1, wherein, when Ris one unit of the polymer precursor without sulfonyl fluoride orsulfonyl chloride, the method further comprises polymerizing themulti-acid monomer to form a multi-acid polymer.
 4. The method of claim1, further comprising: forming a multi-acid membrane for a fuel cellfrom the multi-acid polymer by: converting any remaining sites of themulti-acid polymer to acid form by ion-exchanging the multi-acid polymerwith sulfuric acid solution to form the membrane.
 5. The method of claim1, wherein the multi-sulfonyl halide compound is 1,3,5-benzenetrisulfonyl chloride or 1,3,5-tris[(fluorosulfonyl)]benzene and themulti-acid monomer has the following formula:


6. The method of claim 1, wherein the multi-sulfonyl halide compound isone of benzene-1,3-disulfonyl chloride or benzene-1,2-disulfonylchloride and the multi-acid monomer has the following formula:


7. The method of claim 1, wherein the multi-sulfonyl halide compound isperfluorobutane-1,4-bis-sulfonyl chloride orperfluorobutane-1,4-bis-sulfonyl fluoride and the multi-acid monomer hasthe following formula:

—SO₂—NH—SO₂—(CF₂)₄—SO₃H.
 8. The method of claim 1, wherein themulti-sulfonyl halide compound is1,4-bis(fluorosulfonyloxy)-octafluorobutane and the multi-acid monomerhas the following formula:

—SO₂—NH—SO₂—O—(CF₂)₄—O—SO₃H.
 9. The method of claim 1, wherein themulti-sulfonyl halide compound isbis[2-(fluorosulfonyl)tetrafluoroethyl] ether and the multi-acid monomerhas the following formula:

—SO₂—NH—SO₂—CF₂CF₂—O—CF₂CF₂—SO₃H.
 10. The method of claim 1, wherein themulti-sulfonyl halide compound is1,1,2,2,3,3-hexafluoro-propane-1,3-disulfonyl difluoride and themulti-acid monomer has the following formula:

—SO₂—NH—SO₂—(CF₂)₃—SO₃H.
 11. The method of claim 1, wherein themulti-sulfonyl halide compound is1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexane-1,6-disulfonyl fluoride andthe multi-acid monomer has the following formula:

—SO₂—NH—SO₂—(CF₂)₆—SO₃H.
 12. The method of claim 1, wherein themulti-sulfonyl halide compound is naphthalene-1,2,6-trisulfonyl chlorideand the multi-acid monomer has the following formula:


13. A multi-acid monomer having the following formula:

wherein R is one or more units of a non-SO₂F or non-SO₂Cl portion of apolymer precursor in sulfonyl fluoride or sulfonyl chloride form, X is anon-sulfonyl halide group of a multi-sulfonyl halide compound having aminimum of two acid giving groups, and Y is remaining sulfonyl halidegroups of the multi-sulfonyl halide compound.
 14. The multi-acid monomerof claim 13, wherein the polymer precursor is 4-(trifluoro vinyl)benzene sulfonyl fluoride.
 15. The multi-acid monomer of claim 13,wherein the polymer precursor is p-styrene sulfonyl fluoride/chloride.16. The multi-acid monomer of claim 13, wherein the polymer precursor isperfluoro (3-oxapent-4-ene) sulfonyl fluoride.
 17. The multi-acidmonomer of claim 13, wherein the polymer precursor is ethene sulfonylfluoride.
 18. The multi-acid monomer of claim 13, wherein the polymerprecursor is 2-propene-1-sulfonyl chloride.
 19. A multi-acid polymermade from repeating units of the multi-acid monomer of claim
 13. 20. Amulti-acid membrane made from the multi-acid polymer of claim 19.